Popular Science Monthly/Volume 27/July 1885/The Oldest Air-Breathers
|THE OLDEST AIR-BREATHERS.
WE alluded in the March number of the "Monthly," to the fossil scorpions recently discovered in the Upper Silurian formations of Sweden and Scotland, recognizing them as the most ancient specimens of land or air-breathing animals yet found. The subject has since gained a new interest through the discovery of a still older fossil of an insect, and by these our knowledge of the land of the earth and of some of its inhabitants is carried back by at least two immense geological periods. We therefore give place to a fuller account of the discoveries, with portraits of these newly found oldest inhabitants of the solid part of the globe, collating the facts and borrowing the illustrations from the French and English scientific journals. Scorpions had already been found quite abundantly in the lowest carboniferous strata. The first palaeozoic specimen that came to light (Cyclophthalmus senior) was found in the coal formation of Chombe, Bohemia, and was described by Count Sternberg in 1835. Three years later another scorpion (Microlabis) was described from the same locality. The next discoveries were American, and were made in the coal-measures of Illinois, of two genera which Meek and Worthen described as Eoscorpius (dawn-scorpion) and Mazonia (from Mazon Creek, where they were found). In 1873 Dr. Henry Woodward showed that Eoscorpius remains occurred in the coal-measures of England and in the carboniferous limestone of Scotland; and in 1881 Mr. Benjamin N. Peach described a considerable number of scorpions which had been obtained by the officers of the Geological Survey of Scotland from the lowest carboniferous rocks of the Scottish border. In his paper, which was published in the "Transactions" of the Royal Society of Edinburgh, he pointed out the general resemblance and almost equally high organization of these ancient scorpions and those of the present day, and expressed regret that Messrs. Meek and Worthen had given the name of Eoscorpius to their specimens, "for the dawn of the scorpion family must have been at a much earlier period, and we may hope that their remains will yet turn up in the Devonian and Silurian plant-beds when these come to be thoroughly searched."
This prediction has been verified in the discovery of the Scotch and the Swedish Silurian fossils. The Scotch scorpion was discovered first, by Dr. Hunter, of Carluke, who obtained his specimen from Lesmahagow, in Lanarkshire, in June, 1883; but the Swedish professor, Lindström, although a year later in discovery, anticipated him in announcing it and in publishing the description of his fossil.
In a letter of November 24, 1884, to M. Alphonse Milne-Edwards, Professor Lindström says of his scorpion (Fig. 1): "The specimen is in sufficiently good preservation, and shows the chitinous brown or yellowish-brown cuticle, very thin, compressed, and corrugated by the pressure of the superposed layers. We can distinguish the cephalo-thorax, the abdomen, with seven dorsal laminæ, and the tail, consisting of six segments or rings, the last narrowing and sharpening into the venomous dart. The sculpture of the surface, consisting of tubercles and longitudinal keels, entirely corresponds with that of living scorpions. One of the stigmata on the right is visible, and clearly demonstrates that it must have belonged to an air-breathing animal, and the whole organization indicates that it lived on dry land." Professor Lindström points out, as a feature of great importance in the conformation of the animal, the existence of four pairs of thoracic feet, large and pointed, resembling the feet of the embryos of several other tracheates and animals like the Campodea. This form of feet, he remarks, "no longer exists in the fossil scorpions of the carboniferous formation, the appendices belonging to which resemble those found in the scorpions of our own day." This species has been named Palæophoneus nuncius.
The Scottish specimen (Fig. 2) is described by Mr. Peach in "Nature" as being about an inch and a half long, and lying on its back
Fig. 1.—Fossil Scorpion (Palæophoneus nuncius) found in the Silurian rocks of the Island of Gottland of Sweden. From the photograph sent by Professor Lindström to M. Alphonse Milne-Edwards, (From "La Nature.")
on the stone. "Its exposed ventral surface shows almost every external organ that can be seen in that position, and in this way serves to supplement the evidence supplied by the Swedish specimen. As in the northern individual, the first and second pair of appendages of the cephalo-thorax in the Scottish example are chelate, but the palpi are not quite so robust. The walking-limbs, though not so clumpy as in P. nuncius, also terminate in a single claw-like spike. The arrangement of the sternum shows a large pentagonal plate (metasternite), against which the wedge-shaped coxæ of the fourth pair of walking-limbs abut. The coxæ of the third pair bound the pentagonal plate along its upper margins, and meet in the mid-line of the body, where they are firmly united. The coxæ of the first two pairs, as well as the bases of the palpi, are drawn aside from the center line of the body, showing that, as in recent scorpions, these alone were concerned in manducation, or rather the squeezing out of the juices of the prey; from the circumstance of these being drawn aside, the medial eyes are seen pressed up through the cuticle of the gullet, and a fleshy labrum (camerostome) appears between the bases of the chilicerae.
"Behind the pentagonal plate and the coxæ of the hindmost limbs there succeeds a space shaped like an inverted V, where the test is thin and wrinkled in the line of the long axis of the body. It is just along this line that the trunk or abdomen most easily separates from the cephalo-thorax in recent scorpions, and it is at once apparent that the trunk in this case is as far separated from the cephalo-thorax as it can well be without being detached. Similar longitudinally wrinkled skin is seen to unite the dorsal and ventral scutes up the whole right side of the trunk. At the interior angle of the inverted V there hangs downward a narrow bifid operculum flanked on each side by the combs, which have each a broad triangular rachis set along its lower edge with the usual tooth-like filaments. The combs almost hide the first of the four ventral sclerites, which bear the breathing apparatus in recent scorpions, notwithstanding which all four of these exhibit on their right side undoubted slit-like stigmata at the usual places. The fifth ventral scute of the trunk suddenly contracts posteriorly, and to its narrow end is articulated a long tail of five joints and a poison-gland with a sting. These joints are all constructed on the same principle as those of recent scorpions, and, as the articular surfaces are more highly faceted on the dorsal than on the ventral aspect (a portion of the tail of the specimen lying sidewise allowing of these observations), there can be no doubt that the animal was in the habit of carrying the tail over the head (so to speak), and stinging in the same manner as its recent congeners." These characters are shown in the accompanying illustration (Fig. 2), which is on the same scale as that of the figure of the Swedish example (Fig. 1), viz., about twice the natural size.
The animal is supposed to have wandered to the sea-shore in search of food, and there been imbedded in marine strata. From the completeness of the remains, it is evident that it can not have been carried far out to sea; the rocks of the formation in which the fossil was found abound in Eurypterids, or fossils of a crustacean allied to the king-crab.
Of the recent discovery of earlier Silurian insects, we have the following account given by M. Charles Brongniart to the French Academy of Sciences:
"Fossil insects have been found in the carboniferous strata. The coal-beds of Commentry have furnished some thirteen hundred specimens, and Mr. Scudder has described six specimens that were found in the Devonian beds of New Brunswick; but, until very recently, no representative of that class had been detected in any of the more ancient formations. M. Douvillé, a professor in the School of Mines, has shown me a piece of Middle Silurian sandstone from Jurques, Calvados, bearing a distinct impression of an insect's wing (Fig. 3). The state of preservation is not perfect, but we can still distinguish most of the nervation. The wing, which is about thirty-five millimetres long, belonged to a blattid, an insect of the cockroach family. The humeral field is broad, and upon it may be seen the superior humeral vein; the inferior humeral vein, bifurcated at its extremity; the vitrean or median vein, likewise divided into
|Fig. 3.—Wing of a Fossil Blatta (Palæo-blattina Douvillei). in a piece of Silurian sandstone (natural size).
|Fig. 4.—Restoration of the Fossil Wing.
two branches; the upper and lower discoidal veins, with their very oblique divisions meeting again at the end, just as they may still be seen to do on some living Blattæ; and we can follow the anal vein, which is nearly straight and extends almost to the end of the wing, together with the axillary veins parallel to it. The remarkable feature which distinguishes this impression from the wings of all other blattids, living and fossil, is the length of the anal nervature and the scant width of the axillary held. Among the blattids of the coal period, the Prognoblattina Fritschii (Heer) and the Gerablattina fascigera (Scudder) have a nervation a little resembling that of our Silurian wing. We propose to name this ancestor of the Blattæ, Palæoblattina Douvillei, in honor of Professor Douvillé.
"Geologists regard as identical the sandstones of May and Jurques
Fig. 5.—Living Blattæ, male and female (Blabera claraziana), from Mexico.
in the Calvados, and place them in the Middle Silurian, while the schists of the Island of Gottland belong to the Upper Silurian. Our blatta-wing, then, must be regarded as older than the scorpion described by Professor Lindström and the other similar scorpion from the Upper Silurian of Lanarkshire."
Besides the engraving of the actual fossil wing in Fig. 3, we give in Fig. 4 an ideal restoration of the same; and in Fig. 5, for comparison, a representation of a living blatta from Mexico, the venation of whose wings nearly corresponds with that of the fossil.